Need for measuring temperature in modern machines is prevalent. Temperature sensors of various sorts are known. Continuously monitoring a component's temperature may result in useful information about the component's remaining lifetime. While a multitude of temperature monitoring options may exist, few are appropriate for rotating machinery in harsh environment applications such as engine bearings. For instance, wired sensors including fiber optic sensors, thermocouples, and thermoelectric devices employing the Seebeck effect are not suitable for bearing monitoring because of the continuous rotation around a shaft. Infrared sensors and surface acoustic wave sensors may be suitable options for many wireless applications, but they require line-of-sight, which is often not possible within a bearing housing or other complex temperature monitoring applications. Popular approaches based on active silicon circuits become ineffective at temperatures approaching 300° C. due to the low bandgap of silicon. High-bandgap materials, on the other hand, like silicon carbide or gallium nitride suffer from high cost as well as reliability and repeatability challenges.
Furthermore, active circuits require a power source. Since elevated temperatures are typically detrimental to batteries, energy harvesting or wireless powering schemes would need to be utilized. However, many of these approaches are impracticable in environments of high temperatures.
Therefore, there is a need for a reliable temperature sensor that is small in size, can operate in high temperature environments, and be placed in moving components of a machine.